Linear polyvinyl acetals



Patented Nov. 15, 1949 LINEAR POLYVINYL ACETALS Cecil W. Gayler, Ridley Park, 'Pa., assignor to American Viscose Corporation, Wilmington, Del., a corporation of Delaware Serial No. 48,321

No Drawing. Application September 8,1948,

This invention relates to linear polyvinyl acetalsya method of making them, and the manufacture of shaped articles therefrom. This application is a continuation-in-part of my prior application Serial No. 510,488, filed November 16, 1943, now abandoned.

Heretofore it has been the general practice to, produce polyvinyl acetals by condensation of a polyvinyl alcohol with an aldehyde or aldehydedeveloping polymer in solution in a polar solvent such as an aqueous medium containing a mineral acid catalyst for the reaction, under which conditions the aldehyde has to react with the alcohol in thedissolved state. In order to bring about condensation of the aldehyde with a polyvinyl alcohol in the dissolved state, in any practical length of time, external heat has to be applied for external heat and/or excess aldehyde is used the resulting product has as high as 95% of the -hy-- droxyl groups converted to acetal linkages and, since the use of external heating, or of excess aldehyde, or both, induces the reaction. of one molecule of the aldehyde with two hydroxyl groups each of which is on a difierent chain, the chains are merged into three dimensional groups and the product contains cross-links in an amount such that the product cannot be readily extended.

Useful textile filaments cannot be obtained from polyvinyl acetals containing any appreciable number of cross-links. A cross-linked structure cannot be stretched and therefore orientation of the molecules in the direction of the fiber axis, essential to high tenacity and extensibility in the filaments, and resulting from stretching, cannot be efiected. Fibers formed from the typical polyvinyl acetals of the prior art have so little tensile strength that they can be crumbled between the fingers. The acetals previously available have had the. additional disadvantage that they are 16 Claims. (Cl. 28-82) linear polyvinyl acetals in a period of time not greater than one-half hour, in the'absence of external heat and/or pressure. A further object is to produce directly a solution of a linear polyvinyl acetal suitable for spinning into synthetic fibers, casting to films, etc. An additional object is to produce useful synthetic textile fibers and filaments consisting of a linear polyvinyl acetal and characterized by high tenacity and extensibility.

In accordance with the invention, linear polyvinyl acetals are obtained in from 20 to 30 minutes in the absence of external heat and pressure, by condensing an aldehyde, i. e. formaldehyde or acetaldehyde or their aldehydedeveloping polymers, trioxymethylene or paraldehyde, with a polyvinyl alcohol in suspension in a medium which is a solvent for the acetal formed, but not a solvent for the polyvinyl alcohol, and in which thewater split out during the condensation is soluble.

In practicing the invention, the polyvinyl alcohol and aldehyde are suspended in-1,4-dioxane and hydrogen chloride gas is bubbled continuously through the suspension'until the condensation reaction is completed. For the aldehydes mentioned, the conditions are critical and experiment with a large number of other nonsoluble in a large number of common organic solvents.

One object of the, present invention is to provide a polyvinyl acetal which is entirely free of cross-links between chains. Another object is to provide a fiber-forming polyvinyl acetal capable of accepting stretch whereby the molecules are oriented in the direction of the fiber axis. An-. other object is to provide a method of making of a mixture of 1,4-dioxane and hydrogen chloride gas is necessary for accomplishing. the objects of this invention. I

The reaction of the aldehyde and alcohol in 1,4- ;dioxane hydrogen chloride gas mixture is exothermic and goes to completion rapidly, without the use of external heat; During the course of the reaction, the temperature rises and may reach C.-or so; If desired, outside cooling may be employed toofiset the tendency of'the temperature to'increase, but suchcooling is ontional and not required because exposure of the mass to the'elevated' temperature forthe' extremely short period required for the reaction does not'efiect cross-linking of the chains;

As soon as hydrogen chloride gas is passed into the mixture of polyvinyl alcohol, diox'ane; and

aldehyde, the temperature rises" and a gel is synthetic fibers, or cast tofforin'films.

During the condensation reaction, somewater is split out. The'water'is soluble in-lA-di'oxane and is absorbed thereby. If a suil'icientlyflarge amount of dioxane is 'p'resent,the water oil? will be entirely absorbed thereby and will remain as a constituent of the final solution, in a blend with the 1,4-dioxane. If all of the water is not absorbed by the 1,4-dioxane, as happens when smaller amounts of 1,4-dioxane are used (for example 70 to 85% depending on molecular weight and percent ester groups on the polyvinyl alcohol) the water not absorbed will be saturated by the hydrogen chloride gas, forming hydrochloric acid, which will separate out in the form of a layer, due to the salting out" effect of the hydrogen chloride gas, which salts out the dioxane. In any event, the medium is initially anhydrous and the relatively small amount of water split out during the reaction is insuflicient to dissolve any appreciable quantity of the alcohol. This is in contrast to the eifects obtained when hydrochloric acid as such is added to the reaction and the reaction is carried out in the presence of both the water of the acid and the water formed in the reaction. Polyvinyl alcohol is not soluble in the 1,4-dioxanehydrogen chloride gas mixture in which the condensation is performed, but that mixture is a solvent for the polyvinyl acetal which, under the preferred conditions, is dissolved therein as it is produced, providing a driving force for the reaction.

The final product consists of a resinous solution of a linear polyvinyl acetal of which from 80 to 90% of the hydroxyl groups originally present in the polyvinyl alcohol have been converted to acetal linkages; in a mixture consisting of dioxane and dissolved hydrogen chloride, and which may also contain water in a blend with the dioxane. The acetal has a molecular weight in the neighborhood of 10,000 to 30,000 or higher. The number of hydroxyl groups converted to formal linkages is critical for the production of synthetic fibers and films, and is in the range of from 80 to 90% for a polyvinyl alcohol containing, initially, from up to about ester groups. If too many ester groups, for example, acetate groups, are present in the final acetal, the product has a low softening point and is soluble in a large number of organic solvents. If too many hydroxyl groups are converted to acetal linkages, (some of which are inevitably cross-links) the product is brittle and inextensible; it cannot be oriented by stretching. If the product contains too many hydroxyl groups, it is water-susceptible and fibers made from it are characterized by high shrinkage in water at laundering temperatures. The present invention makes possible the production of a linear acetal containing a controlled proportion of acetate groups, free hydroxyl groups, and acetal linkages.

Polyvinyl alcohols are generally produced by complete or partial hydrolysis of a polyvinyl ester. The present process may be used for the production of acetals from polyvinyl alcohols resulting from complete or partial hydrolysis of an ester, depending on the purpose for which the acetal is intended. When the resinous solution of the acetal is to be spun into synthetic filaments, the starting polyvinyl alcohol is preferably one which is free of, or substantially free of, ester groups. For other purposes, for instance when the acetal is to be used as a finishing or coating agent for textiles or the like, or in the fabrication of massive molded articles, cinematographic film, laminated sheets, etc., the starting alcohol may contain up to 10% ester groups, for example, acetate groups.

when the polyvinyl acetal produced according to my improved process is obtained from a polyvinyl alcohol which is substantially free from ester groups, highly desirable artificial filaments or films may be obtained by spinning or casting the solution directly into suitable. coagulating media.

This may be accomplished by spinning the solution of the linear polyvinyl acetal according to either the wet or dry spinning processes. In the former case, the solution may be cast or spun through an appropriate spinneret or jet directly into a-suitable coagulating bath at room temperature. Such a bath may consist of any medium in which the solvent for the resin is soluble, and in which the resin is insoluble. Thus, for example, the resinous solution may be spun into water through a 300 or 500-hole spinneret having holes of from 2.5 to 3 mils in size, at about 25 C., using a regularviscose gear spinning pump to propel the viscous solution. The coagulating bath may consist of water either alone or containing adjuvants, such as plasticizing agents, delustrants, dyes, pigments, etc.

The dry spinning process is also applicable, in which-case the resinpus solution containing the linear polyvinyl acetal is spun or cast into an evaporative atmosphere, such as .warm air, or other inert gas, in order to cause evaporation of the solvent.

My tests have shown that, whereas fibers obtained by spinning the typical polyvinyl acetals of the prior art are coarse and brittle, and substantially inextensible, samples thereof even breaking apart readily upon subjection to a light pull between the fingers, the fibers obtained by spinning the linear polyvinyl acetals prepared according to my-invention as described herein, are thermoplastic, smooth, and tough. They can be given a stretch of 100% or more between godets at 25 C., and may be subjected to a further afterstretch of at least another 100% in a steam cell, at to C. The stretched fibers show by characteristic X-ray diffraction patterns of orientation of the molecules along the fiber axis, and the tensile strength of the fibers is increased considerably thereby. Such filaments have been found to have a dry tenacity of up to at least 4 grams per denier, and a wet tenacity of up to at least 3.3 grams per denier; dry elongation of from about 10 to 18 and wet elongation of about 10 to 20%.

The linear polyvinyl acetals of my invention are insoluble in practically all common organic solvents. The following table illustrates the results obtained when a linear polyvinyl formal obtained according to my invention was tested for solubility in various solvents.

I-iusolnble; S-soluble; SW-swells; P. S.partly soluble.

The following specific examples are given for the purpose of illustrating my invention.

Example I Eqinvalent amounts of powdered polyvinyl alcohol (containing 1.5% acetate groups) and triowmethylene were suspended, by stirring, in anhydrous 1,4-dioxane. forming a suspension of about 20% total solids. Hydrogen chloride gas was bubbled through the suspension whereupon the suspended material went into solution, forming a clear gel at first, which, upon continued stirring and passage of hydrogen chloride, became a viscous solution. There was considerable evolution of heat, raising the temperature to about 60 C. The reaction was complete in about 20-30 minutes. About 80-90% of the hydroxyl groups of the polyvinyl alcohol were converted to formal linkages, and the formal had a molecular weight of about 17,000. In this instance, where the dioxane was used in an amount of 80%, the resulting product contained a small amount of water from the reaction which separated and was withdrawn as hydrochloric acid after the reaction was completed. The final product consisted of a resinous solution of the acetal in 1,4-dioxane containing dissolved hydrogen chloride. 7 Q 1 Example II Twenty-two parts of powdered polyvinyl alcohol (obtained by complete hydrolysis of polyvinyl acetate) and 15 parts of formaldehyde were suspended, by stirring, in 300 parts of 1,4-dioxane. Hydrogen chloride gas was bubbled through I the suspension, whereupon the suspended material went into solution, forming a clear gel at first. Upon continued stirring, and passing of hydrogen chloride gas the gel was dissolved, forming a clear viscous solution. The reaction was complete in 20-30 minutes, during which time the temperature rose to about 60 C. All of the water formed in the reaction was absorbed by the 1,4-dioxane and there was no sep-. aration of water. The product was homogeneous and consisted of a clear liquid amber solution of the acetal in a mixture consisting of the 1,4-di- I oxane, dissolved hydrogen chloride, and water blended with the 1,4-dioxane. About 90% of the hydroxyl groups of the polyvinyl alcohol were converted to formal linkages, and the formal had a molecular weight of 27,000.

Example III The resinous solution of the polyvinyl acetal obtained according to the process described in Example I was spun through a multiple-hole spinneret into an aqueous coagulating bath at 25 C. The coagulated filaments were withdrawn from the bath and given a stretch of 100% between godets at 25 C., after which theywere stretched an additional 100% in a steam cell at 90 C.

In contrast to the results obtained when poly-.

poses.

It was attempted to perform the reaction in a large number of other solvents, hydrogen chloride gas being bubbled through the solvent in each case, and the conditions being similar to those of Example H. In every instance, a reaction tool: place. but the products formed were useless. The results obtained with the various solvents tried are listed in the, following table:

Ethyl methylketoneformed a suspension of swelled particles which darkened on standing. Tetrahydrofuran-black gel. Ethanol-kacetoneblack gel.

} Cellosolve acetate-formed white translucent gel which turned black on standing for a few days. Dimethoxytetraethylene glycol-black gel. Diethyl Cellosolve-black liquid-two layers, one

layer of water and one of suspended gel particles.

.AcetalVery dark, two layers--resin layer not suitable for spinning; comprises a. suspension of jelled particles.

Any variation or modification of the invention as described above which conforms to the spirit of the invention is intended to be included within the scope of the appended claims.

I claim:

1. A linear polyvinyl acetal resulting from the condensation of a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcohols concontaining up to 10% of ester groups and trioxy-v methylene, in suspension in an initially anhydrous non-polar medium consisting of 1,4-dioxane in the presence of hydrogen chloride gas distributed through the medium, and in; the absence of external heat and pressure.

3. A solution adapted to be directly spun into water to form artificial fibers capable of being stretched to effect orientation of the molecules in the direction of the fiber axis and comprising the resinous solution of a linear polyvinyl acetal obtained by suspending a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcohols containing up .to 10% of ester groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the'absence of external heat and pressure.

4. A solution to be directly spun into water to form artificial fibers capable of being stretched to eilect orientation of the molecules in the direction of the fiber axis and comprising the resinous solution of a polyvinyl formal obtained by suspending a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcohols containing.

' up to 10% of ester groups and trioxymethylene in 1,4-dioxane, and continuously bubbling hydrogen tion being carried out in k chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

5. A process for the production of a linear polyvinyl acetal comprising suspending -a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcoholscontaining up to-10% of ester groups andan aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene,'and paraldehyde in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the polyvinyl alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

6. The process for the production of a linear polyvinyl formal comprising suspending a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcohols containing up to 10% of ester groups and trioxymethylene in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reacbeing carried out in the absence of external heat and pressure.

'7. A, stretched synthetic fiber showing, by characteristic X-ray diffraction patterns, orientation of hydrogen chloride medium, and in the absence of external heat and 8. gasdistributedthroughthe tained by suspending a polyvinyl alcohol which of the molecules along the fiber axis, and comprising a linear polyvinyl acetal, said acetal being substantially entirely free of cross-links between molecular chains and obtained by suspending a polyvinyl alcohol containing up to 10% of esier groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, and ontinuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

8, A stretched synthetic fiber showing, by characteristic X-ray diffraction patterns, orientation of the molecules along the fiber axis, and comprising a linear polyvinyl formal, said formal being substantially free of cross-links between molecu-- lar chains and obtained by suspending a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols containing no ester groups and polyvinyl alcohols containing up to 10% of ester groups and trioxymethylene in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reacthe absence of external heat and pressure. y

9. A linear polyvinyl acetal resulting from the condensation of a polyvinyl alcohol which does not contain estergroups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, ti'ioxymethylene, and paraldehyde, in suspension in an initially anhydrous non-polar medium consisting of 1,4-dioxane, in the presence of hydrogen chloride gas distributed through the medium, and in the absence of external heat and pressure.

10. A linear polyvinyl acetal resulting from the condensation of a polyvinyl alcohol containing up to 10% of ester groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde, in suspensmn in an initially anhydrous non-polar medium consisting of 1,4-dioxane, in the presence,

does not contain ester groups and an aldehyde selectedfrom the group consisting of'formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

12. A solution adapted to be directly spun into water to form artificial fibers capable of being stretched to effect orientation of the molecules in the direction of the fiber axis and comprising the resinous solution of a linear polyvinyl acetal obtained by suspending a polyvinyl alcohol containing up to 10% of ester groups and an aidehyde selected from the group consisting of formaldehyde, aoetaldehyde, trioxymethylene, and paraldehyde. in 1,4-dioxane,- and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of eirternal'heat and pressure.

13. A process for the production of a linear polyvinyl acetal comprising suspending a polyvinyl alcohol which does not contain ester groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, andcontinuously bubbling hydrogen chloride gas through the suspension until the reaction between the polyvinyl alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure. A

14. A process for the production of a linear polyvinyl acetal comprising suspending a polyvinyl alcohol containing up to 10% of ester groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the polyvinyl alcohol and aldehyde is completed, the

reaction being carried out in the absence of ex-' ternal heat and pressure.

15. A stretched synthetic fiber showing, by characteristic X-ray diffraction patterns, orientation of the molecules along the fiber axis, and comprising a linear'polyvinyl aeetal, said acetal being substantially entirely free of cross-Jinks between molecular chains and obtained by suspend-- ing a polyvinyl alcohol selected from the group consisting of polyvinyl alcohols which do not contain ester groups and polyvinyl alcohols containing up to 10% of ester groups and an aldehyde selected from the group consisting of formaldehyde, acetaldehyde, trioxymethylene, and paraldehyde in 1,4-dioxane, and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

16. A stretched synthetic fiber showing, by characteristic x-ray difiraction patterns, orientation of the molecules along the fiber axis, and

comprising a linear polyvinyl acetal. said acotal 9 V being substantially entirely free 01' cross-links betrioxymethylene, and paraldehyde in 1,4-dioxane,

and continuously bubbling hydrogen chloride gas through the suspension until the reaction between the alcohol and aldehyde is completed, the reaction being carried out in the absence of external heat and pressure.

CECIL W. GAYLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,080 Robertson A118. 25, 1936 2,035,939 Belloc Mar. 31, 1936 Number Number Name Date 4 Kuehn June 16, 1936' Starck Sept. 22, 1936 'Ihielklng Apr. 11, 1939 Dorough Feb. 16, 1943 Buchsbaum Aug. 31, 1943 Land Aug. 31, 1943 Swan Aug. 22, 1944 Sharkey Mar. 5, 1946 FOREIGN PATENTS Country Date a Great Britain Feb. 18, 1933 Great Britain May 18, 1934 Great Britain Apr. 8, 1938 OTHERREFERENCES Ser. No. 715,003, (A. P. C) pub. l 27,

Y Certificate of Correction Patent No. 2,487,864 L November 15, 1949 CECIL W. GAYLER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 24, for resinpus read resinous; column 5, line 20, for 17,000 read 27,000;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 7th day of March, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

